In recent years, various techniques related to speeding up of wireless communication have been developed. For example, IEEE 802.11n (hereinafter referred to as 11n), which is one of standard specifications for wireless communication, employs the MIMO (Multiple Input Multiple Output) scheme in which a transmitter and a receiver each have a plurality of antennas and perform communication assuming transmission paths between the antennas as virtual communication channels independent of each other, thereby achieving significant improvement of throughput compared to a communication scheme such as the existing IEEE 802.11a (hereinafter referred to as 11a).
In this manner, the improvement of throughput has been achieved to a certain extent in 11n. However, a further speeding up is required to handle the increasing amount of information of contents.
In studies of a new communication scheme, it is important to consider compatibility with another communication scheme. For example, it is preferred that 11n has backward compatibility with the existing communication standards such as 11a. Therefore, wireless communication devices capable of receiving 11n packets are often designed to be capable of receiving both packets of 11a packets and 11n packets.
Further, when a wireless communication device on the receiving side finishes receiving a data packet, it transmits ACK, which is a response signal, to a wireless communication device on the transmitting side in order to notify that the packet has been successfully received. In 11a and 11n, for example, the allowed time from the end of reception of the data packet to the start of transmission of the ACK is specified to be 16 μs as SIFS (Short Inter Frame Space).